1. Field
The present invention relates to a light emitting diode (LED), and more particularly, to an LED capable of improving light extraction efficiency by reducing light loss due to an electrode structure formed at an upper portion of the LED.
2. Discussion of the Background
GaN-based light emitting diodes (LEDs) are currently used in a variety of applications such as full-color LED display devices, LED traffic lights and white LEDs. Recently, it has been expected that high-efficiency white LEDs will substitute for fluorescent lamps. Particularly, the efficiency of the whit LEDs has reached the level similar to that of typical fluorescent lamps.
A GaN-based LED is generally formed by growing epitaxial layers on a substrate such as sapphire, and comprises an N-type semiconductor layer, a P-type semiconductor layer and an active layer interposed therebetween. Meanwhile, an N-electrode pad is formed on the N-type semiconductor layer, while a P-electrode pad is formed on the P-type semiconductor layer. The LED is driven by being electrically connected to an external power source through the electrode pads.
The GaN-based semiconductor layers are generally grown on a single crystalline substrate such as sapphire, and a single LED is finally completed through a chip separation process. At this time, since the single crystalline substrate is separated along its crystal plane, it typically has a rectangular shape. Generally, the shape of the substrate in a final LED defines the shape of a light emitting structure, e.g., the shape of a mesa, the shape of an electrode pad and the shape of extension portions extending from the electrode pad. For example, extension portions extending from electrode contact portions so as to enhance current spreading has been disclosed in U.S. Pat. No. 6,650,018, and these extension portions typically extend in a straight line along a rectangular edge of the rectangular shape.
By using an extension portion(s) extending from an electrode pad, it is possible to improve the effect of current spreading into an LED, thereby enhancing the efficiency of the LED. However, since a material, e.g., Cr, having a poor reflecting property is used as a lower structure of the electrode pad and the extension portion extending therefrom, there is a large amount of light loss due to light absorption at lower portions of the electrode pad and/or the extension portion. The light loss serves as a primary factor for obstructing the enhancement of the light extraction efficiency of the LED. Although a number of studies have been conducted to reduce the light loss by decreasing the entire area of an electrode pattern having an extension portion, the decrease of the entire area of the electrode pattern may have a bad influence on the current spreading effect of an LED. Particularly, it may be difficult to implement a large-area LED chip.